Health Care Costs Payable - Components of Change in Health Care Costs Payable (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period, net	$ 6,879
Less: Claims paid
Health care costs payable, end of the period, net	7,593
Health Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Health care costs payable, beginning of the period	6,879	$ 6,147
Less: Reinsurance recoverables	5	4
Health care costs payable, beginning of the period, net	6,874	6,143
Acquisition	444	0
Add: Components of incurred health care costs
Current year	40,777	39,657
Prior years	(448)	(511)
Total incurred health care costs	40,329	39,146
Less: Claims paid
Current year	34,198	33,032
Prior years	5,865	5,253
Total claims paid	40,063	38,285
Add: Premium deficiency reserve	1	6
Health care costs payable, end of the period, net	7,585	7,010
Add: Reinsurance recoverables	8	4
Health care costs payable, end of the period	7,593	7,014
Premium deficiency reserve	1	6
Health Care Benefits
Less: Claims paid
Benefit costs recorded in other insurance liabilities	31	31
Corporate / Other
Less: Claims paid
Benefit costs recorded in other insurance liabilities	$ 173	$ 213